Vapor-liquid contact apparatus



United States Patent VAPOR-LIQUID CONTACT APPARATUS David G. Reynolds,Jackson Heights, N. Y.

Application October 11, 1950, Serial No. 189,501

Claims. (Cl. 261-114) This invention relates to vapor-liquid contactapparatus and more particularly to a unique downcomer structure which ismost advantageously used in combination with double cross-flow decks inlarger diameter towers.

It is a general object of this invention to provide the proper hydraulicbalance on a large deck and to thereby insure proper liquid distributionover the deck.

A second object is to provide a means whereby separate liquid streamsmay be individually and separately guided downwardly through the decksof a distillation tower.

A third object of my invention is to alter the design of multiplefractionating decks to assure even liquid and vapor distribution,thereby greatly improving the efficiency of the decks.

An additional object is to permit the easy fabrication of internalstripping sections in large diameter towers.

Other and further objects and features of the invention will be apparentto those skilled in the art on a consideration of the accompanyingdrawings and following specification wherein are disclosed severalexemplary embodiments of the invention with the understanding that suchmodifications may be made therein as fall within the scope of theappended claims without departing from the spirit of the invention.

Fig. l is a vertical central section through a tower having decksconstructed in accordance with the present invention.

Fig. 2 is a horizontal section taken on line 22 of Fig. 1 and lookingdownwardly as indicated by the arrows.

Fig. 3 is a vertical central section through a tower having a modifiedform of my invention.

Fig. 4 is a perspective view with parts in section of a modified form ofmy invention.

Fig. 5 is a horizontal section taken along lines 5-5 of Fig. 4.

Fig. 6 is a horizontal section taken along lines 6-6 of Fig. 4.

It is generally recognized that the flowing liquid gradient across afractionating column deck increases as the diameter of the towerincreases because of the length of the liquid travel. The effect of thisgradient is to permit uneven vapor flow through the decks because of theunequal liquid head at opposite sides of the deck. This effect isgenerally compensated for by the use of double cross-flow decks with twoparallel flow liquid streams or multiple flow decks with multipleparallel liquid streams in larger towers. A double cross-flow deck ischaracterized by the admission of liquid to opposite ends of an upperdeck, and its passage toward the center of this upper deck to adowncomer which carries the liquid to a central reservoir on the nextlower deck. Thus it can be seen that since the liquid will generallyflow only halfway across the diameter of the tower, there will be acorrespondingly lower difference in liquid head between opposite ends ofthe liquid path. Multiple liquid flow towers are a substantialimprovement over the single cross-flow decks but have lead toinefliciencies caused by unequal liquid distribution between the variousliquid flow streams. Unless the liquid down flow and rising vaporstreams are divided proportionately, inefficient and imperfect contactwill result, reducing the deck efficiency.

Fig. 1 shows a double-cross flow deck constructed in accordance with oneembodiment of my invention in which the number 10 represents a shell ofa bubble tower having a vapor oil-take 11, and'a reflux conduit 12.

, 2,698,746 Patented Jan. 4, 1955 Conduit 12 is divided into two lines13 and 14 controlled respectively by valves 15 and 16. Lines 13 and 14feed to opposite sides of the top deck 17 of the tower 10. The decks 17,18, 19, 20 and 21 each hear one or more bubble caps 22 and theirassociated risers 23 in each liquid flow stream. In the arrangementshown the tower may be best described as made up of a plurality of pairsof decks, it being apparent that the physical structure of the pair 17and 18 is identical to that of the pair 19 and 20 etc. It is convenientto arbitrarily refer to deck 17 as the upper and deck 18 as the lowerdeck of the pair.

Upper deck 17 has weirs 24 which form reservoirs 25 at opposite ends ofthe deck. At the center of deck 17 is a central downcomer structureincluding a pair of upstanding downcomer plates 26, each surmounted by aweir 27 the purposes of which is to maintain a liquid level on the deck17. The downcomer plates 26 extend downwardly to a point adjacent to thenext lower deck 18. The weirs 28 on deck 18 are laterally spaced fromthe lower edge of the downcomer plates 26. Deck 18 bearing a pluralityof caps 22 and risers 23, has at its opposite outer edges, twoupstanding weirs 29 each surmounting a lateral downcomer 39. At thecenter of deck 18 there is mounted an upstanding plate 31 secured inliquid tight relationship to the deck 18 and extending upwardly withinthe confines of the downcomer i. e. between the downcomer plates 26.This plate 31 divides the lower deck 13 into two separate liquidcompartments. 3

The nature of hydraulic unbalance which exists in a standard cross-flowtower without a means of dividing the liquid downflow may be brieflydescribed by reference to Fig. l. The decks in such a tower will notnormally contain the improved downcomer of Fig. l but may contain muchof the other structure. Reflux liquid to deck 17 can be split equally bythe reflux distributor including pipes 12, 13 and 14 and valves 15 and16. it has been observed that due to disturbances in the flow arisingfrom external circumstances the distribution of liquid from the liquidreservoir in the central downcomer may be uneven. It is then possible tohave a much greater liquid flow over side A of deck 13 than is foundover side B. This results in all of the vapor passing through side B dueto the lower pressure drop therein.

To illustrate more clearly the undesirable conditions which occur ondecks 19 and 29 when the hereinbefore disclosed invention is not used,we adopt the following notation:

P1=pressure of vapor below deck 20. This is the same under side A andside B.

P2=pressure of vapors above deck 20, side B.

Ps pressure of vapors above deck 19, side A and side B.

P4=pressure of vapors above deck 20, side A.

Assume a pressure drop of 6 of downflow liquid through decks 19 and 2d,P1-Ps=6". The pressure drop of the vapor flowing through side B would bedivided approximately equal so that P1P2=3" and P2P3=3". However this isnot true of side A. Although the same pressure diilerential existsthrough either side of decks 19 and 20 together, a larger portion of thedifferential could be taken in the liquid over the bubble caps on deck19, side A. This will give a condition where P4-P3 is less than 3" andP1P is greater than 3". For example, if P4P3=2, then P1-P4:4" willsatisfy the pressure conditions between Pi-P3=6". The pressure existingabove side A and side B of deck 20 is then such that the pressure, P2,in side B is l" greater than the pressure P4, in side A. In this case, al" liquid-differential could exist over the inlet weirs to deck 2%, thatis, inlet weir to side 9 would have a 1" head whereas side B could haveno The pressure drop through deck 19, side A(P4--P3), will be determinedby the head of liquid over the top of the bubble cap slots. Very littlevapor would come through side A; only that vaporized by heat transferthrough the deck woud pass upwardly. This would not create anynoticeable pressure drop through the bubble decks in deck 1%, side A.

Once this unequal flow started. it would continue down h the column,thereby preventing the decks from operating with equal and eflicientvapor-liquid contact thereby greatly reducing the desired efficiency.

To insure perfect tray hydraulics and adequate liquid submergence of thebubble cap, my improved downcomer has been placed as shown in Fig. 1. Itis liquid tight and is sufficiently high to prevent liquid from oppositesides of the deck from mixing. It is generally as high as the liquid onthe deck and may be higher. By means of this bafile, liquid may be keptseparated in the various sides of the tower thereby insuring acontrolled, even flow distribution. This method and apparatus is alsoadapted to trip and quadruple cross-flow decks.

Fig. 3 shows how this invention may be used to incorporate separatestripping section into a standard distillation tower. Tower 40 has decks41, 42, 43, 44, 45, 46, etc., constructed in similar fashion to those ofFig. 1, and provided with bubble caps 58. Each of the decks is dividedinto two parts by a central upstanding plate 47 which extends from thebottom of a lower deck 46, upwardly within the confines of the centraldowncomer, past the next upper deck 45, and to the under part of thedeck 44. Thus the tower 40 is divided into two independent sections: onesection 48 and a separate section 49. These sections are separate fromone another and may have independent and separate liquid downfiowstreams of different compositions and independent and separate vaporstreams of ditferent compositions.

To illustrate, oil feed to the tower 40 may be admitted through line 50after having passed through heater 51. The oil descends through thedecks of the separate section 49 to the tower bottom 52 where it isseparately collected. Steam may be admitted through line 53. Strippedliquid is reboiled in the circuit including line 54, pump 55 andreboiler 56 and is returned to the tower above section 48. It thenpasses downwardly to chamber 57. Chamber 57 and chamber 52 are separatedby partition 58 which may be extended to the under side of deck 46 ifdesired. Reboiled liquid is removed from the tower through line 59,which may be interconnected with line 54 if circulating reboiling isdesired.

In Fig. 4 the tower 60 has a liquid dividing means resting on a lowerdeck 61 and bounded by the downcomer structure. Deck 61 is provided withouter downcomers 61b and a plurality of bubble caps 61a. The downcomeris made up of upstanding central downcomer plates 62 and 63 which aresubstantially identical. Each of these plates extends from lower deck 61upwardly to the bottom of the next upper deck, not shown. Plate 62, forexample has a substantially straight upper edge 64, and substantiallystraight side edges 65. One end 66 of the lower edge of the plate 62 issecured in liquid tight manner to deck 61. The other end 67 is raisedabove the deck 61 so that a passageway is formed between the plate andthe deck. The raised end 67 of plate 62 is opposed to the lower end 66of plate 63.

Plates 62 and 63 are joined at their midsection by divider plates 68 and69 having an apex or crest at 70. These plates extend outwardly anddownwardly from apex 70 to a point not lower than the level of theraised edge 67. The end 66 of plate 62 is joined to end 66 of plate 63by dam 71. Weirs 72 extend laterally across the deck 61 on either sideof the downcomer plates 62 and 63 and form liquid reservoirs 73 and 74.

A portion of the downflow plates 62 and 63 is left open to permit thepassage of vapor through opening 77 so that no great pressuredifferential will exist between the portions of the decks divided by thedownflow.

In operation, liquid falling from an upper deck, not shown, will bedivided into two equal portions by the centrally located apex 70. Oneportion will pass downwardly along divider plate 68 to the receivingzone 75 of the reservoir 73. This liquid will then accumulate and passunder edge 67 of plate 62, through the reservoir 73 and over weir 72.Edge 67 extends below the upper edge of weir 72.

It is thus possible to evenly divide liquid passing downwardly throughthe column in a manner which is positive and simple, and to therebyobtain a suitable solution to the problems of unfavorable hydraulicgradient.

I claim:

1. In a distillation column containing a plurality of pairs ofvapor-liquid contact decks in vertically spaced relation and whereinliquid on alternate decks flows in opposite directions with respect tothe centers thereof,

the liquid on said upper deck flowing toward a common central downcomerstructure, the improvement which comprises a central downcomer in theupper deck of a pair of said decks, an upstanding plate secured to thelower deck of said pair of decks and extending upwardly within theconfines of said downcomer completely separating the liquid on oppositesides of said downcomer, said plate extending laterally to the directionof liquid flow on said lower deck whereby each of the descending streamsof liquid in said downcomer is independently guided to a separatereservoir in said lower deck.

2. In a distillation column containing a plurality of pairs ofvapor-liquid contact decks in vertically spaced relation and whereinliquid on alternate decks flows in opposite directions with respect tothe centers thereof, the liquid on said upper deck flowing toward acommon central downcomer structure, the improvement which comprises acentral downcomer in the upper deck of a pair of said decks, anupstanding plate secured to the lower deck of said pair of decks andextending upwardly within the confines of said downcomer to theunderside of the lower deck of the next higher pair of decks completelyseparating the liquid on opposite sides of said downcomer, said plateextending laterally to the direction of liquid flow on said deckswhereby each of the descending streams of liquid in said downcomer isindependently guided to a separate reservoir in said lower deck, and thevapors ascending from each deck are maintained in separate courses asthey pass upwardly through the decks.

3. In a distillation column containing a plurality of pairs ofvapor-liquid contact decks in vertically spaced relation and whereinliquid on alternate decks flows in opposite directions with respect tothe center thereof, the liquid on said upper deck flowing toward acommon central downcomer structure, the improvement which comprises acentral downcomer in the upper deck of a pair of said decks, a centrallylocated liquid partitioning plate structure in said downcomer, saidplate structure positioned on the lower deck of said pair of decks, saidplate structure extending upwardly within the confines of saiddowncomer, said plate structure having an upwardly pointed crest, saidcrest extending across said downcomer at the center thereof and havingits horizontal projection in a vertical plane substantially parallel tothe direction of liquid flow on said upper deck, and completelyseparating the liquid on opposite sides of said downcomer, whereby eachof the descending streams of liquid in said downcomer is independentlyguided to a separate reservoir in said lower deck said liquid in saiddowncomer is divided into two controlled streams, means for passing eachof said controlled streams to an independent portion of the lower deckof said pair of decks, and means for distributing each of said streamsover its respective lower deck.

4. In a distillation column containing a plurality of pairs ofvapor-liquid contact decks in vertically spaced relation and whereinliquid on alternate decks flows in opposite directions with respect tothe centers thereof. the liquid on said upper deck flowing toward acommon central downcomer structure, the improvement which comprises acentral downcomer in the upper deck of a pair of said decks, anupstanding plate secured to the lower deck of said pair of decks andextending upwardly within the confines of said downcomer terminatingbelow the underside of the lower deck of the next higher pair of decksand completely separating the liquid on opposite sides of saiddowncomer, said plate extending laterally to the direction of liquidflow on said decks and completely separating the liquid on oppositesides of said downcomer, whereby each of the descending streams ofliquid in said downcomer is independently guided to a separate reservoirin said lower deck.

5. In a distillation column containing a plurality of pairs ofvapor-liquid contact decks in vertically spaced relation and whereinliquid on alternate decks flows in opposite directions with respect tothe center thereof, the liquid on said upper deck flowing toward acommon central downcomer structure, the improvement which comprises, acentral downcomer in the upper deck of a pair of said decks, a centrallylocated liquid partitioning plate structure in said downcomer, saidplate structure positioned on the lower deck of said pair of decks,extending upwardly within the confines of said downcomer and completelyseparating the liquid on opposite sides of said downcomer, whereby eachof the descending streams of liquid in said downcomer is independentlyguided to a separate reservoir in said lower deck.

References Cited in the file of this patent UNITED STATES PATENTS 6Smith June 23, 1931 Monro Aug. 16, 1932 Suess Dec. 15, 1936 Thomwy Feb.9, 1937 Eckey Nov. 9, 1943 Hutcheson et a1. Mar. 21, 1944 Dennis Jan. 9,1945 Linder July 11, 1950 Parkinson June 26, 1951 Dice Oct. 9, 1951

